Turbine engines are used as the primary power source for various kinds of aircraft. The engines may also serve as auxiliary power sources that drive air compressors, hydraulic pumps, and industrial electrical power generators. Most turbine engines generally follow the same basic power generation procedure. Compressed air is mixed with fuel and burned, and the expanding hot combustion gases are directed against stationary turbine vanes in the engine. The vanes turn the high velocity gas flow partially sideways to impinge onto turbine blades mounted on a rotatable turbine disk. The force of the impinging gas causes the turbine disk to spin at high speed. Jet propulsion engines use the power created by the rotating turbine disk to draw more air into the engine, and the high velocity combustion gas is passed out of the gas turbine aft end to create forward thrust. Other engines use this power to turn one or more propellers, electrical generators, or other devices.
Because fuel efficiency increases as engine operating temperatures increase, turbine engine blades and vanes are typically fabricated from high-temperature materials such as nickel-based superalloys. However, although nickel-based superalloys have good high-temperature properties and many other advantages, they may be susceptible to corrosion, oxidation, thermal fatigue, and/or foreign particle impact when exposed to harsh working environments during turbine engine operation. In such cases, the turbine engine blades and vanes may need to be repaired, such as by welding, by a diffusion brazing process or by a combination of both welding and diffusion brazing.
Diffusion brazing processes typically employ a braze alloy mixture that includes a base alloy material (also referred to as a “high-melt alloy”) and a braze alloy material (also referred to as “a low-melt alloy”). The high-melt alloy is usually a material that is substantially similar in composition to the material of the component being repaired, while the low-melt alloy typically comprises an alloy powder including boron or silicon as melting-point depressants and a relatively small amount of (e.g., a volume fraction gamma prime of less than about 40) or no gamma prime elements or other solid solution strengthening alloying elements other than chromium. The low-melt alloy typically has a melting temperature that is lower than that of the high-melt alloy. After a slurry coating of the braze alloy mixture is applied to a damaged area on the turbine component and subjected to heat treatment in a vacuum furnace, the braze alloy mixture melts and heals cracks and builds up material loss on the damaged area.
Although the aforementioned processes are suitable for performing repairs on certain components, they may not be suitable for repairing other components, such as those made of single crystal superalloys. In particular, known conventional braze alloy mixtures may contain higher level of boron or silicon. These melting-point depressants may be limited to repairing components that may be exposed to turbine inlet temperatures up to about 1450° C. because the resultant braze repaired areas may not retain desirable properties at higher operating temperatures. In addition, due to addition of high level of boron and/or silicon, brittle centerline borides may form in braze joints or surface areas which may decrease the ductility thereof.
Accordingly, an improved braze alloy mixture suitable for repairing cracks in a components intended for exposure to turbine inlet temperatures higher than 1450° C. is desired. In particular, it is desirable to have a braze alloy mixture and a method for repairing a component that does not cause the formation of brittle phases in the repaired areas. In addition, it is desirable for the method to be relatively simple and inexpensive to implement. Furthermore, other desirable features and characteristics of the inventive subject matter will become apparent from the subsequent detailed description of the inventive subject matter and the appended claims, taken in conjunction with the accompanying drawings and this background of the inventive subject matter.